Mobile communication terminal and transmission-bit-rate detection method

ABSTRACT

A mobile communication terminal which receives convolutionally encoded data that is convolutionally encoded information of a speech channel transmitted from a base station and detects a transmission bit rate selected at the base station by decoding the data. The mobile communication terminal comprises a rate estimation unit which estimates the transmission bit rate selected at the base station and outputs an estimated transmission bit rate, a decoding unit which decodes the convolutionally encoded data transmitted from the base station and outputs decoded data and predetermined types of results of decoding, a convolutional re-encoding unit which convolutionally re-encodes the decoded data and outputs re-encoded data, and a rate detection unit which detects whether the estimated transmission bit rate is correct or not based on the decoded data and the predetermined types of results of decoding.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a mobile communicationsystem, and more particularly to a mobile communication terminal whichdetects a transmission bit rate that is selected at a base station and atransmission-bit-rate detection method.

[0003] In the field of mobile communication, access methods which assignmaximum users to limited frequency resources are desired. These accessmethods include, for example, Frequency-Division Multiplex Access(FDMA), Time-Division Multiplex Access (TDMA) and Code-DivisionMultiplex Access (CDMA). In the FDMA and the TDMA, one radio stationoccupies one radio channel and slot. On the other hand, in the CDMA, awide-band radio channel is shared among many users by adding proper codeto a signal.

[0004] Presently, the mobile communication systems which employ the FDMAand the TDMA are in practical use. On the other hand, the mobilecommunication system which employs the CDMA is desired because it isrobust against both interference and disturbance and can keep privacy.This is because the proper code is added to the signal in the CDMA.

[0005] 2. Description of the Related Art

[0006] A conventional transmission-bit-rate detection method whichdetects a transmission bit rate that is selected at a base station for aconventional mobile communication system is explained below.

[0007] Generally, when the base station communicates with a mobilecommunication terminal, speech data and control data are transmittedthrough a speech channel in the mobile communication system whichemploys the CDMA. The speech channel can carry the speech data and thecontrol data at any bit rate among 9.6 kbps, 4.8 kbps, 2.4 kbps and 1.2kbps. The data is transmitted at a variable transmission bit rate usingthese four bit rates.

[0008] The base station adds error detection code, for example, CyclicRedundancy Check (CRC), and tail bits to information bits of the speechchannel. The CRC is only added when the transmission bit rate is either9.6 kbps or 4.8 kbps. Next, the base station adds convolutional code forerror correction to the information bits of the speech channel to whichthe CRC and the tail bits are added and generates transmission symbols.Then, the base station outputs the transmission symbols at thedesignated bit rate among 9.6 kbps, 4.8 kbps, 2.4 kbps and 1.2 kbps.When the designated bit rate is 9.6 kbps, then transmission symbols areoutput one time. When the designated bit rate is 4.8 kbps, thentransmission symbols are repeatedly output twice. When the designatedbit rate is 2.4 kbps, then transmission symbols are repeatedly outputthree times. When the designated bit rate is 1.2 kbps, then transmissionsymbols are repeatedly output four times. This is because the samenumber of bits is needed to detect the transmission bit rate at themobile communication terminal.

[0009] Next, these transmission symbols are interleaved and scrambledwith long Code which is a user identification code and enablessynchronization at the mobile communication terminal. Then, powercontrol bits are added. The power control bits control strength of aradio wave for each mobile communication terminal. A weak radio wave istransmitted to the mobile communication terminal near the base stationand a strong radio wave is transmitted to the mobile communicationterminal far from the base station to equalize the strengths of theradio waves received by the mobile communication terminals. After all ofthe processes described above are ended, the base station spreadsspectrum of the transmission symbols over a wide band. Next, the basestation modulates the transmission symbols and transmits thetransmission symbols.

[0010] The mobile communication terminal of the mobile communicationsystem which employs a spread spectrum method operates as follows todetect the transmission bit rate.

[0011]FIG. 1 shows main parts used to detect the transmission bit ratefor the conventional mobile communication terminal.

[0012] At the mobile communication terminal, first, received data isdemodulated and its spectrum is inverse-spread. Next, long Code isgenerated based on information from a sync channel and inverse spectrumspread data is descrambled using the information. Then, descrambled datais deinterleaved. As a result, received symbols are reproduced. Thereceived symbols are supplied to four Viterbi decoders, such as a9.6-kbps Viterbi decoder 101, a 4.8-kbps Viterbi decoder 102, a 2.4-kbpsViterbi decoder 103 and a 1.2-kbps Viterbi decoder 104, which areconnected in parallel as shown in FIG. 1. Each decoder executes Viterbidecoding at each bit rate and outputs decoded data.

[0013] Convolutional re-encoders, such as a 9.6-kbps convolutionalre-encoder 105, a 4.8-kbps convolutional re-encoder 106, a 2.4-kbpsconvolutional re-encoder 107 and a 1.2-kbps convolutional re-encoder108, re-encode the decoded data. A selector 109 compares the data whichis re-encoded by the convolutional re-encoders with the received data.Then, the selector 109 detects the transmission bit rate based oncomparison results which have minimum errors. The bit rate of theconvolutional re-encoder which outputs re-encoded data with minimumerrors is the transmission bit rate and the decoded data of the Viterbidecoder which has the same bit rate as that of the convolutionalre-encoder with minimum errors is output to a codec. The conventionalmobile communication terminal detects the transmission bit ratedescribed above.

[0014] However, in the conventional mobile communication terminal, thefour Viterbi decoders, consisting of the 9.6-kbps Viterbi decoder 101,the 4.8-kbps Viterbi decoder 102, the 2.4-kbps Viterbi decoder 103 andthe 1.2-kbps Viterbi decoder 104, shown in FIG. 1 decode the receiveddata simultaneously at all bit rates. Moreover, the four convolutionalre-encoders, consisting of the 9.6-kbps convolutional re-encoder 105,the 4.8-kbps convolutional re-encoder 106, the 2.4-kbps convolutionalre-encoder 107 and the 1.2-kbps convolutional re-encoder 108, re-encodethe decoded data simultaneously at all bit rates.

[0015] In the conventional mobile communication terminal, the Viterbidecoding and the convolutional re-encoding at all bit rates are executedsimultaneously. Therefore, this results in both increase of a circuitscale and increase of consumption power.

SUMMARY OF THE INVENTION

[0016] It is a general object of the present invention to provide amobile communication terminal in which the above disadvantages areeliminated.

[0017] A more specific object of the present invention is to provide amobile communication terminal which enables a small-sized mobilecommunication terminal based on reduction of the circuit scale andreduction of the consumption power of the mobile communication terminal.

[0018] The above objects of the present invention are achieved by amobile communication terminal which receives convolutionally encodeddata that is convolutionally encoded information of a speech channeltransmitted from a base station and detects a transmission bit rateselected at the base station by decoding the data. The mobilecommunication terminal comprises a rate estimation unit which estimatesthe transmission bit rate selected at the base station and outputs anestimated transmission bit rate, a decoding unit which decodes theconvolutionally encoded data transmitted from the base station andoutputs decoded data and predetermined types of results of decoding, aconvolutional re-encoding unit which convolutionally re-encodes thedecoded data and outputs re-encoded data, and a rate detection unitwhich detects whether the estimated transmission bit rate is correct ornot based on the decoded data and the predetermined types of results ofdecoding.

[0019] As the transmission bit rate is estimated by the mobilecommunication terminal, a plurality of decoders for all bit rates is notnecessary. A plurality of re-encoders is also not necessary for the samereason. Therefore, the simultaneous decoding of the received data byfour decoders at all bit rates and the simultaneous re-encoding of thedecoded data by four re-encoders at all bit rates are not necessary.This results in the small-sized mobile communication terminal based onthe reduction of the circuit scale and enables the reduction of theconsumption power of the mobile communication terminal.

[0020] The above objects of the present invention are achieved by atransmission-bit-rate detection method for a mobile communicationterminal which receives convolutionally encoded data that isconvolutionally encoded information of a speech channel transmitted froma base station. The transmission-bit-rate detection method comprises arate estimation step which estimates the transmission bit rate selectedat the base station and outputs an estimated transmission bit rate, adecoding step which decodes the convolutionally encoded data transmittedfrom the base station and outputs decoded data and predetermined typesof results of decoding, a convolutional re-encoding step whichconvolutionally re-encodes the decoded data and outputs re-encoded data,and a rate detection step which determines whether the estimatedtransmission bit rate is correct or not based on the decoded data andthe predetermined types of results of decoding.

[0021] As the transmission bit rate is estimated by the rate estimationstep, a plurality of decoders for all bit rates is not necessary. Aplurality of re-encoders is also not necessary for the same reason.Therefore, the simultaneous decoding of the received data by fourdecoders at all bit rates and the simultaneous re-encoding of thedecoded data by four re-encoders at all bit rates are not necessarybecause the transmission-bit-rate detection method is executed. Thisresults in the small-sized mobile communication terminal based on thereduction of the circuit scale and enables the reduction of theconsumption power of the mobile communication terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other objects, features and advantages of the present inventionwill become more apparent from the following detailed description whenread in conjunction with the accompanying drawings, in which:

[0023]FIG. 1 shows main parts used to detect a transmission bit rate fora conventional mobile communication terminal;

[0024]FIG. 2 is a transmission data generation process at a base stationin a mobile communication system;

[0025]FIG. 3 is a frame structure of a speech channel;

[0026]FIG. 4 is a block diagram of a general convolutional encoder;

[0027]FIG. 5 is an example of a convolutional encoder when k equals one,m equals two and n equals two in the general convolutional encoder;

[0028]FIG. 6(a) is a state transition diagram of the convolutionalencoder;

[0029]FIG. 6(b) is a trellis diagram of the state transition diagram ofthe convolutional encoder;

[0030]FIG. 7 is a block diagram of the mobile communication terminal ofthe present inventions;

[0031]FIG. 8 is an outline of an operation of a CPU 11;

[0032]FIG. 9 shows main components of the CPU 11 or a DSP 21 in an LSIcircuit 1 which executes the transmission-bit-rate detection;

[0033]FIG. 10 is a detailed structure of a Viterbi decoder 17;

[0034]FIG. 11 is a Viterbi decoding algorithm for received symbols;

[0035]FIG. 12 is a structure of a multirate deinterleaver addressgenerator 47; and

[0036]FIG. 13 is a transmission-bit-rate detection algorithm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] A transmission-bit-rate detection method for a mobilecommunication terminal of a first embodiment of the present invention,which mobile communication terminal detects the transmission bit rateselected at the base station, will be explained below.

[0038]FIG. 2 shows a transmission data generation process at a basestation in a mobile communication system. When the base stationcommunicates with a mobile communication terminal, speech data andcontrol data are transmitted through a speech channel in the mobilecommunication system which employs CDMA. The speech channel can carrythe speech data and the control data with any bit rate among 9.6 kbps,4.8 kbps, 2.4 kbps and 1.2 kbps. The data is transmitted with a variabletransmission bit rate using these four bit rates.

[0039]FIG. 3 shows a frame structure of the speech channel. At the basestation, for example, a cyclic code F for error detection is added toinformation bits in a CRC addition step S1 of FIG. 2, when atransmission bit rate of either 9.6 kbps or 4.8 kbps is selected asshown in FIGS. 3(a) and (b). The error detection by the cyclic code iscalled CRC(Cyclic Redundancy Check). A polynomial expression of datareceived by the mobile communication terminal is divided by a generationpolynomial. The received data is checked as to whether it is encodeddata or not according to whether a remainder is equal to zero or not.

[0040] Next, in a tail bit addition step S2 of FIG. 2, tail bits areadded to the information bits when the transmission bit rate is either2.4 kbps or 1.2 kbps or to the information bits with the CRC when thetransmission bit rate is either 9.6 kbps or 4.8 kbps as shown in FIGS.3(a), (b), (c) and (d). A convolutional encoder in the base station isinitialized by adjusting all tail bits to be zero.

[0041] Next, in a convolutional encoding step S3 in FIG. 2, aconvolutional code for error correction is added to the information bitsto which the tail bits are added in order to generate transmissionsymbols. In the convolutional encoding process, information of pastblocks affect a present convolutional encoding block.

[0042]FIG. 4 shows a block diagram of a general convolutional encoder.In the general convolutional encoder, a serial input informationsequence is converted into k-bit parallel information blocks. Each k-bitparallel information block is converted into an n(>k)-bit paralleloutput block by a linear combinational logic circuit using past datablocks stored in delay elements D. Then an output convolutional codesequence which is serially converted from the n-bit parallel outputblocks is output.

[0043]FIG. 5 shows an example of the convolutional encoder when k equalsone, m equals two and n equals two in the general convolutional encoder.The output sequence {y_(k)}={y_(1k) y_(2k)} is expressed using the inputsequence {x_(k)} as follows.

y _(1k) =x _(k) +x _(k−2) , y _(2k) =x _(k) +x _(k−1) +x _(k−2)

[0044] When X, Y₁, Y₂ are respectively converted from {x_(k)}, {y_(1k)},{y_(1k)} by a Z transform, then,

Y ₁ =G ₁(z)X, Y ₂ =G ₂(z)X

G ₁(z)=1+Z ⁻² , G ₂(z)=1+Z ⁻¹ +Z ⁻²

[0045] G₁(z) and G₂(z) are called generator polynomials of theconvolutional code. Other generator polynomials are defined for otherconvolutional encoders in the same manner as shown above.

[0046]FIG. 6(a) shows a state transition diagram of the convolutionalencoder. FIG. 6(b) shows a trellis diagram of the state transitiondiagram of the convolutional encoder.

[0047] In the convolutional encoder shown in FIG. 5, if the inputsequence is {1001 . . . }, the output sequence of convolutional code is{11 01 11 11 . . . }.

[0048] Next, the explanation of FIG. 2 will be continued. In arepetition of transmission symbols step S4 of FIG. 2, the base stationgenerates the transmission symbols, which are convolutionally encoded,according to the designated bit rate among 9.6 kbps, 4.8 kbps, 2.4 kbpsand 1.2 kbps. When the designated bit rate is 9.6 kbps, then thetransmission symbols are generated one time. When the designated bitrate is 4.8 kbps, then the transmission symbols are repeatedly generatedtwice. When the designated bit rate is 2.4 kbps, then the transmissionsymbols are repeatedly generated three times. When the designated bitrate is 1.2 kbps, then the transmission symbols are repeatedly generatedfour times. This is because the same number of bits is needed to detectthe transmission bit rate at the mobile communication terminal. Thetransmission bit rate is selected at the base station, for example, in ahigh-density order of speech data from 9.6 kbps to 1.2 kbps. Because theselected transmission bit rate is not communicated to the mobilecommunication terminal, the mobile communication terminal must detectthe transmission bit rate to reproduce a speech signal.

[0049] Next, in an interleaving step S5 of FIG. 2, these transmissionsymbols are interleaved. The interleaving rearranges an order of thesymbols and is effective to raise an error correction performance forburst errors.

[0050] Next, in a long Code generation step S6, a decimator step S7 anda scrambling step S8 of FIG. 2, output symbols of the interleaving stepare scrambled using long Code which is a user identification code andenables synchronization at the mobile communication terminal. Then, inthe decimator step S9 and a power control bit insertion step S10 of FIG.2, power control bits are added to the scrambled data and transmissiondata to be sent the mobile communication terminal is generated. Thepower control bits control strength of a radio wave to be transmitted toeach mobile communication terminal. A weak radio wave is transmitted toa mobile communication terminal near the base station and a strong radiowave is transmitted to a mobile communication terminal far from the basestation to equalize the strengths of the radio waves received by themobile communication terminals.

[0051] After all of the processes described above from S1 to S10 arefinished, in a spread spectrum modulation step S11 of FIG. 2, the basestation spreads spectrum of the transmission data over a wide band.Then, the base station modulates the transmission data and transmits thetransmission data. As spread spectrum communication has a characteristicthat energy of each band unit is low, the spread spectrum communicationis robust against both interference and disturbance from other systems.The base station transmits the transmission data to each mobilecommunication terminal as mentioned above.

[0052] Next, the mobile communication terminal of the present inventionwill be explained. FIG. 7 shows a block diagram of the mobilecommunication terminal of the present invention.

[0053] The mobile communication terminal shown in FIG. 7 is mainly madeup of an RF unit 2, an A/D·D/A converter 3, an LSI circuit 1 and aspeech controller 6. The RF unit 2 receives the radio wave from the basestation. The A/D·D/A converter 3 converts an analog signal from the RFunit 2 into a digital signal, i.e., received data. The LSI circuit 1,which is equipped with a CPU 11, executes various kinds of dataprocessing which will be described later. The speech controller 6executes speech processing by a codec. In the mobile communicationterminal, the LSI circuit 1 executes signal processing for key data fromkey pads 5 or speech data from a microphone 8 which is processed by thespeech controller 6. The LSI circuit 1 also transmits data to the basestation and displays characters on an LCD. The LSI circuit 1 and thespeech controller 6 also execute signal processing for speech data orcontrol data from the base station, display characters on the LCD andreproduce sound through speakers 7.

[0054] Next, a structure and a function of the LSI circuit 1 will beexplained. The LSI circuit 1 is made up of the CPU 11, a ROM/RAM 12, afree logic circuit 13, a long Code generator 15, a Viterbi decoder 17, aDSP 21, a demodulator 14 and a deinterleaver 16. The CPU 11, the ROM/RAM12, the free logic circuit, the long Code generator 15 and the Viterbidecoder 17 are connected through an internal bus. The DSP 21 isconnected to the CPU 11 through an interface. The demodulator 14demodulates the received data supplied from the A/D·D/A converter 3 andthe deinterleaver 16 generates the received symbols. The Viterbi decoder17 executes the Viterbi decoding for the received symbols. The CPU 11and the DSP 21 detect the transmission bit rate which is selected at thebase station and the Viterbi decoder executes the Viterbi decodingaccording to the detected transmission bit rate.

[0055] The CPU 11 or the DSP 21 controls an operation for thetransmission-bit-rate detection. The CPU 11 or the DSP 21 estimates thetransmission bit rate which is selected at the base station and detectsa correct transmission bit rate by decoded results according to anestimated transmission bit rate.

[0056] The ROM/RAM 12 stores a program to detect the transmission bitrate and data to be read or written during execution of the program.Because the DSP 21 can also execute such a program, the ROM/RAM 12 maybe allocated in the DSP 21.

[0057] The free logic circuit 13 displays the characters from the keypads 5 on the LCD 4 and executes other functions.

[0058] The long Code generator 15 generates the long Code to synchronizewith the received data according to information transmitted through async channel.

[0059] The demodulator 14 has a RATE receiver which receives thereceived data from the A/D·A/D converter 3 and demodulates the receiveddata. The demodulator 14 also executes an inverse spread spectrumoperation. Then, the demodulator 14 descrambles the received dataaccording to the long Code from the long Code generator 15.

[0060] The deinterleaver 16 converts the order of the temporallyinterleaved data into a proper order and generates the received symbols.

[0061] The Viterbi decoder 17 executes the Viterbi decoding of thereceived symbols from the deinterleaver 16 according to the transmissionbit rate estimated in the CPU 11. This Viterbi decoder 17 can executethe Viterbi decoding at any rate among 9.6 kbps, 4.8 kbps, 2.4 kbps and1.2 kbps.

[0062] When the LSI circuit 1 in the mobile communication terminal shownin FIG. 7 receives data, which is processed as shown in FIG. 2,transmitted from the base station, the LSI circuit 1 executes anoperation as shown in FIG. 8. FIG. 8 shows an outline of an operation ofthe CPU 1. FIG. 9 shows main components of the CPU 11 or the DSP 21 inthe LSI circuit 1, which CPU 11 or DSP 21 executes thetransmission-bit-rate detection. In this embodiment of the presentinvention, the CPU 11 executes the transmission-bit-rate detection.

[0063] In the LSI circuit 1, first, the demodulator 14 executes inversespread spectrum demodulation at an inverse spread spectrum demodulationstep S21 and the descrambling based on the long Code generated by thelong Code generator 15 at a descramble step S22. The deinterleaver 16generates the received symbols by deinterleaving the received data atthe deinterleave step S23.

[0064] The received symbols are supplied to the Viterbi decoder 17 and arate estimation block 32 in the CPU 11 shown in FIG. 9. The rateestimation block 32 estimates the transmission bit rate which isselected among 9.6 kbps, 4.8 kbps, 2.4 kbps and 9.6 kbps at the basestation. The multirate Viterbi decoder 17 executes the Viterbi decodingat the estimated bit rate and supplies decoded results to aconvolutional re-encoder 31. The convolutional re-encoder 31 re-encodesthe decoded results and supplies re-encoded data to the multirateViterbi decoder 17. The Viterbi decoder 17 compares the received symbolswith the re-encoded data and supplies a comparison result to a ratedetermination block 33. The rate determination block 33 detects whetherthe estimated transmission bit rate is correct or not based on thecomparison result. For example, when the rate determination block 33detects that the estimated transmission bit rate is correct, the Viterbidecoder 17 supplies the decoded data using the estimated transmissionbit rate to the speech controller 6. On the other hand, when the ratedetermination block 33 detects that the estimated transmission bit rateis not correct, the rate estimation block 32 changes the estimate of thetransmission bit rate. Then, the Viterbi decoder 17 repeats the Viterbidecoding at both a Viterbi decoding step S24 and a rate indication anddetermination step S25 until the rate determination block 33 detectsthat the estimated transmission bit rate is correct.

[0065] In the mobile communication terminal of this embodiment of thepresent invention, the transmission-bit-rate detection is executed asdescribed above.

[0066] At the steps S24 and S25, when the rate determination block 33detects that the estimated transmission bit rate is not correct, therate estimation block 32 doubles or halves the estimate of thetransmission bit rate. Then, the Viterbi decoder 17 may repeat theViterbi decoding at the Viterbi decoding step S24 and the rateindication and determination step S25 until the rate determination block33 detects that the estimated transmission bit rate is correct. Forexample, first, the Viterbi decoder 17 executes the Viterbi decoding atthe transmission bit rate of 4.8 kbps. When the rate determination block33 detects that the estimated transmission bit rate is not correct, therate estimation block 32 changes the next estimate of the transmissionbit rate into either 9.6 kbps or 2.4 kbps.

[0067] Next, the transmission-bit-rate detection executed by the Viterbidecoder 17, the CPU 11 and the DSP 21 will be precisely explained.

[0068]FIG. 10 shows a detailed structure of the Viterbi decoder 17. Inthis embodiment of the present invention, the CPU 11 executes thetransmission-bit-rate detection.

[0069] The Viterbi decoder 17 is made up of a branch metric generator41, a multirate ACS operation block 42, a path memory 43, a decoded datamemory 44, a controller 45, a rate determination block 46 and amultirate deinterleaver address generator 47. The Viterbi decoder 17executes the Viterbi decoding for the received symbols at apredetermined transmission bit rate.

[0070]FIG. 11 shows a Viterbi decoding algorithm for the receivedsymbols which are encoded by the encoder shown in FIG. 5. An inputinformation sequence {x_(k)} is convolutionally encoded into aconvolutional code sequence {y_(1k)y_(2k)}. When an error sequence{e_(1k)e_(2k)} occurs during transmission, a receiver receives areceived sequence {z_(1k)z_(2k)}={y_(1k)+e_(1k), y_(2k)+e_(2k)}. TheViterbi decoder 17 detects a maximum likelihood input sequence using theViterbi decoding algorithm shown in FIG. 11.

[0071] Next, a function of each circuit element which forms the Viterbidecoder 17 will be explained. The branch metric generator 41 calculatesbranch metrics which are needed to execute the Viterbi decoding for thereceived symbols. The branch metric λ is;

λ_(ikjk)={(Z _(1k)

i _(k))+(Z _(2k)

j _(k))}

[0072] The multirate ACS operation block 42 is mainly made up of anadder, a path metric memory, a comparator and a selector. The adder addsthe calculated branch metric to the pre-calculated branch metric so thatthe path metric is calculated. The path memory stores the path metric.The comparator compares two path metrics when the two paths are mergedat a state S_(ij). Then, the selector selects a maximum likelihood pathand outputs the maximum likelihood input sequence in reverse order. Theselector also outputs a Yamamoto Quality bit which shows whether adifference between a path metric of a selected path and the path metricis greater than a predetermined value or is smaller than thepredetermined value.

[0073] The path memory 43 stores the input sequence which is decoded bythe multirate ACS operation block 42 in an output order.

[0074] The decoded data memory 44 rearranges the input sequence storedin the path memory 43 into the proper order and outputs the decodeddata.

[0075] The controller 45 controls the Viterbi decoder 17 to startexecution of decoding according to a start message from the CPU 11 orthe DSP 21 and to send an end message after finishing decoding. Thecontroller 45 also outputs a comparison result of the cyclic code whichis the CRC result shown in FIG. 10 and a comparison result, which is thestatus shown in FIG. 10, between the re-encoded data by theconvolutional re-encoder 31 and the received symbols before decoding bythe Viterbi decoder 17.

[0076] The rate determination block 46 sets rate information which is adesignated transmission bit rate by the CPU 11 or the DSP 21.

[0077]FIG. 12 shows a structure of the multirate deinterleaver addressgenerator 47. The multirate deinterleaver address generator 47 is madeup of a 9-bit counter 51, a 1-bit shifter 52, a 2-bit shifter 53 and anadder 55. The 9-bit counter 51 operates synchronously with a clocksignal designated by the CPU 11 and predetermined data is loadedtherein. The multirate deinterleaver address generator 47 divides a9-bit count value [8:0] supplied from the 9-bit counter 51 into 6-bitdata and 3-bit data. The 1-bit shifter 52 shifts the divided 6-bit data[5:0] left and makes 7-bit data. The 2-bit shifter 53 shifts the divided6-bit data [5:0] left and makes 8-bit data. The adder 54 adds both the7-bit data and the 8-bit data and outputs 9-bit data which is 6 timesthe original 6-bit data [5:0]. The adder 55 adds the 9-bit data and the3-bit data [8:6] which was a reminder of the previously divided 9-bitcount value [8:0] and outputs an address to the deinterleaver 16. Themultirate deinterleaver address generator 47 can generate thedeinterleaver address at all four transmission bit rates.

[0078]FIG. 13 shows a transmission-bit-rate detection algorithm which isexecuted by the Viterbi decoder 17 and the CPU 11 of the embodiment ofthe present invention.

[0079] The received symbols generated by the deinterleaver 16 aresupplied to the Viterbi decoder 17 and the rate estimation block 32 inthe CPU 11 shown in FIG. 9. The rate estimation block 32 estimates thetransmission bit rate which is selected at the base station. Then, oneof the transmission bit rates among 9.6 kbps, 4.8 kbps, 2.4 kbps and 1.2kbps is set to the Viterbi decoder 17 in the step S31. First, theestimate of the transmission bit rate is the transmission bit rate whichwas used in the previous Viterbi decoding.

[0080] Next, the Viterbi decoder 17 executes the Viterbi decoding forthe received symbols at the estimated transmission bit rate in the stepS32. The Viterbi decoding algorithm will be explained with FIG. 11. Aninput information sequence {x_(k)} is convolutionally encoded into aconvolutional code sequence {y_(1k)y_(2k)}. When an error sequence{e_(1k)e_(2k)} occurs during transmission, the Viterbi decoder 17receives a received sequence {z_(1k)z_(2k)}={y_(1k)+e_(1k),y_(2k)+e_(2k)}. When a received sequence is {01, 10, 00, 00, 01, 10},the Viterbi decoder 17 detects a proper path which is the correct inputinformation sequence {x_(k)}. The Viterbi decoder 17 uses the receivedsequence and a path which starts from a state S₀₀ at a point of time k=0and ends at the state S₀₀ through paths in a trellis diagram.

[0081] First, the branch metric generator 41 in the Viterbi decoder 17calculates the branch metric which is a Hamming distance between thereceived sequence {z_(1k)z_(2k)} and each branch (i_(k)j_(k)) shown inFIG. 11. The multirate ACS operation block 42 calculates the pathmetrics at a point of time k when paths are merged at S_(ij) at eachpoint of time k (k=1, 2, 3, 4, 5). The comparator compares the pathmetrics and the selector selects a survival path which has a minimumpath metric. Then other paths which are shown with marks X in FIG. 11are deleted. Figures with a parenthesis shows the path metric. The pathsare deleted as mentioned above. Therefore one survived path has aminimum path metric. This path is the maximum likelihood path. As aresult, a sequence (1, 1, 0, 1, 0, 0) is detected as a correct inputsequence. At the same time, a convolutional code sequence (11, 10, 10,00, 01, 11) and an error sequence (10, 00, 10, 00, 00, 01) are output.

[0082] The controller 45 in the Viterbi decoder 17 supplies the decodedresults to the re-encoder 31. The re-encoder 31 re-encodes the decodedresults and supplies re-encoded data to the controller 45. Thecontroller 45 compares the re-encoded data and the received symbolsbefore decoding by the Viterbi decoder 17 and generates the status. Thisstatus and the CRC result using the cyclic code are supplied to the ratedetermination block 33 in the step S32.

[0083] At the same time, the multirate ACS operation block 42 outputsthe path metric of the selected path and Yamamoto Quality bit whichshows whether a difference between path metrics is greater than apredetermined value or is smaller than the predetermined value in thestep S32.

[0084] The rate determination block 33 detects whether the estimatedtransmission bit rate is correct or not. For example, when the result ofthe CRC is correct in a step S33, the rate determination block 33determines that the estimated transmission bit rate is correct in a stepS38. When the result of the CRC is not correct in the step S33 and theYamamoto quality bit is greater than the predetermined value in a stepS34, the rate determination block 33 determines that the estimatedtransmission bit rate is correct in the step S38. When the result of theCRC is not correct in the step S33, the Yamamoto quality bit is smallerthan the predetermined value in the step S34 and a symbol error shown bythe status is smaller than 60 in a step S35, the rate determinationblock 33 determines that the estimated transmission bit rate is correctin the step S38. When the result of the CRC is not correct in the stepS33, the Yamamoto quality bit is smaller than the predetermined value inthe step S34, the symbol error shown by the status is greater than 60 inthe step S35 and the path metric value is smaller than 20 k in a stepS36, the rate determination block 33 determines that the estimatedtransmission bit rate is correct in the step S38. Then, the decoded datais supplied to the DSP 21 and the controller 6.

[0085] On the other hand, when the result of the CRC is not correct inthe step S33, the Yamamoto quality bit is smaller than the predeterminedvalue in the step S34, the symbol error shown by the status is greaterthan 60 in the step S35 and the path metric value is greater than 20 kin the step S36, the rate estimation block 32 determines that theestimated bit rate is not correct in a step S37. Then, the rateestimation block 32 halves or doubles the estimate of the transmissionbit rate in the step S31. Then, the Viterbi decoder repeats the Viterbidecoding until the transmission bit rate is fixed in the step S38.

[0086] As the transmission bit rate which is selected at the basestation is estimated by the CPU 11 and the DSP 21 in the mobilecommunication terminal of the embodiment of the present invention, aplurality of decoders for all bit rates is not necessary.

[0087] As the CPU 11 and the DSP 21 determine whether the estimatedtransmission bit rate is correct or not based on various kinds ofinformation, a plurality of decoders and convolutional re-encoders forall bit rates is not necessary.

[0088] Therefore, the simultaneous decoding at all bit rates and thesimultaneous re-encoding at all bit rates are not executed. This resultsin the small-sized mobile communication terminal based on the reductionof the circuit scale and enables the reduction of the consumption powerof the mobile communication terminal.

[0089] The present invention is not limited to the specificallydisclosed embodiments, and variations and modifications may be madewithout departing from the scope of the present invention.

[0090] The present application is based on Japanese priority applicationNo.10-147760 filed on May 28, 1998, the entire contents of which arehereby incorporated by reference.

What is claimed is:
 1. A mobile communication terminal which receivesconvolutionally encoded data that is convolutionally encoded informationof a speech channel transmitted from a base station and detects atransmission bit rate selected at the base station by decoding the data,the mobile communication terminal comprising: a rate estimation unitwhich estimates said transmission bit rate selected at the base stationand outputs an estimated transmission bit rate; a decoding unit whichdecodes said convolutionally encoded data transmitted from the basestation and outputs decoded data and predetermined types of results ofdecoding; a convolutional re-encoding unit which convolutionallyre-encodes the decoded data and outputs re-encoded data; and a ratedetection unit which detects whether the estimated transmission bit rateis correct or not based on the decoded data and the predetermined typesof results of decoding.
 2. The mobile communication terminal as claimedin claim 1, wherein said decoding unit comprises: an operation unitwhich calculates branch metrics for executing a Viterbi decoding of theconvolutionally encoded data; and a Viterbi decoder which executes theViterbi decoding at the estimated transmission bit rate based on thebranch metrics.
 3. The mobile communication terminal as claimed in claim1, wherein said rate estimation unit comprises a first part whichdetermines the estimated transmission bit rate as a proper transmissionbit rate when the estimated transmission bit rate is detected to becorrect and changes the estimated transmission bit rate when theestimated transmission bit rate is detected not to be correct, and asecond part which makes said decoding unit repeatedly to execute saidViterbi decoding until the estimated transmission bit rate is detectedto be correct.
 4. The mobile communication terminal as claimed in claim3, wherein said rate estimation unit changes the estimated transmissionbit rate to twice or half thereof when the estimated transmission bitrate is detected not to be correct and makes said decoding unitrepeatedly to execute said Viterbi decoding until a changed estimatedtransmission bit rate is detected to be correct.
 5. The mobilecommunication terminal as claimed in claim 1, wherein said decoding unitstarts said Viterbi decoding according to a start message and outputs anend message after said Viterbi decoding is finished.
 6. The mobilecommunication terminal as claimed in claim 1, wherein the predeterminedtypes of results of decoding include a CRC value, a Yamamoto Quality bitand a path metric.
 7. The mobile communication terminal as claimed inclaim 1, wherein the estimated transmission bit rate which is output bysaid rate estimation unit is the transmission bit rate which was usedfor said Viterbi decoding before presently executing said Viterbidecoding.
 8. A transmission-bit-rate detection method for a mobilecommunication terminal which receives convolutionally encoded data thatis convolutionally encoded information of a speech channel transmittedfrom a base station, the method comprising: a rate estimation step whichestimates said transmission bit rate selected at the base station andoutputs the estimated transmission-bit-rate; a decoding step whichdecodes said convolutionally encoded data transmitted from the basestation and outputs decoded data and predetermined types of results ofdecoding; a convolutional re-encoding step which convolutionallyre-encodes the decoded data and outputs re-encoded data; and a ratedetection step which detects whether the estimated transmission-bit-rateis correct or not based on the decoded data and the predetermined typesof results of decoding.
 9. The transmission-bit-rate detection methodfor a mobile communication terminal as claimed in claim 8, wherein saiddecoding step comprises: an operation step which calculates branchmetrics for executing a Viterbi decoding of said convolutionally encodeddata; and a Viterbi decoding step which executes said Viterbi decodingat the estimated transmission bit rate based on said branch metrics. 10.The transmission-bit-rate detection method for a mobile communicationterminal as claimed in claim 8, wherein said rate estimation stepcomprises: a decision step which determines the estimated transmissionbit rate as a proper transmission bit rate when the estimatedtransmission bit rate is detected to be correct; and an execution stepwhich changes the estimated transmission bit rate when the estimatedtransmission bit rate is detected not to be correct and makes saiddecoding step repeatedly to execute said Viterbi decoding until theestimated transmission bit rate is detected to be correct.
 11. Thetransmission-bit-rate detection method for a mobile communicationterminal as claimed in claim 10, wherein said rate estimation stepchanges the estimated transmission bit rate to twice or half thereofwhen the estimated transmission bit rate is detected not to be correctand makes said decoding step repeatedly to execute said Viterbi decodinguntil a changed estimated transmission bit rate is detected to becorrect.
 12. The transmission-bit-rate detection method for a mobilecommunication terminal as claimed in claim 8, wherein said decoding stepstarts said Viterbi decoding according to a start message and outputs anend message after said Viterbi decoding is finished.
 13. Thetransmission-bit-rate detection method for a mobile communicationterminal as claimed in claim 8, wherein the predetermined types ofresults of decoding include a CRC value, a Yamamoto Quality bit and apath metric.
 14. The transmission-bit-rate detection method for a mobilecommunication terminal as claimed in claim 8, wherein the estimatedtransmission bit rate which is output by said rate estimation step isthe transmission bit rate which was used for said Viterbi decodingbefore presently executing said Viterbi decoding.